As ccook said, if you've already gone a couple days without the caffeine, you should be close to getting over the withdrawal, so don't give up!
I quit drinking Diet Coke because I wanted to give up the artificial sweetener. Some days, I really miss the sweetness and the carbonation, and I found a great substitute is Club Soda (w/o sodium) and Juice (apricot nectar or grape juice are my favs). I do about 2 parts club soda to 1 part juice.